1. Field of the Invention
The present invention relates to a precoat film forming method.
2. Description of the Related Art
Generally, in manufacture of semiconductor integrated circuits, film forming and pattern etching are carried out repeatedly for a silicon substrate such as a semiconductor wafer or others and many desired elements are formed.
Meanwhile, for a lower layer of a wiring layer for enabling wiring between the elements and electric contact of the elements, for the purpose of suppressing interdiffusion between Si of the substrate and the wiring material or for the purpose of preventing peeling from the primary coat, a barrier metal is used. For the barrier metal, a material having not only a low electric resistance but also an outstanding corrosion resistance must be used. As a barrier metal material for satisfying such as request, a TiN film is especially apt to be used frequently.
To form a barrier metal of a TiN film, generally a very thin Ti film is formed by plasma CVD and nitride-treated and then a TiN film is formed by thermal CVD using TiCl4 and NH3 gas.
Here noted that the thermal CVD means forming a film by thermochemical reaction without using a plasma.
The process temperature at the time of forming the Ti film must be controlled particularly strictly so as to highly keep the film characteristics in the same way as with forming of a general thin film.
On the surface of a loading table for loading a semiconductor wafer, a precoat film composed of a TiN film is generally formed beforehand for the purpose of holding the thermal intra-surface uniformity of the wafer and preventing metal contamination caused by the metallic element included in the loading table. The precoat film is removed every cleaning inside the film forming device, so, when it is cleaned, a precoat film is thinly deposited on the surface of the loading table as a pretreatment prior to actual forming of a film on the wafer.
Meanwhile, the precoat film is formed, for example, in a high temperature zone such as about 680° C. and as mentioned above, when it formed once, it is used continuously over a long period of time until the inside of the film forming device is cleaned next. In this case, when a so-called idling period which is not used for the film forming process occurs, the temperature is lowered to a temperature at which the quality of the precoat film is not changed, for example, about 300 to 500° C. and the precoat stands by.
The temperature changing operation and temperature stabilization operation of the loading table require a lot of time, so that it is desirable to keep the loading table temperature at the process temperature of TiN film forming from the viewpoint of improving the throughput. However, if the loading table is exposed at a high temperature, for example, about 680° C., the precoat film is degenerated due to a very small quantity of outer gas in the processing container and a very small quantity of leak gas, and the emissivity and transmission factor are changed. After all, although the temperature is controlled in the same way, heat is easily radiated from the loading table due to changing of the emissivity and transmission factor. Thereby, the supply electric energy is increased and the wafer temperature is apt to become higher than expected.
FIG. 7 is a graph showing the condition at this time and it shows changes of the film quality (specific resistance) when a precoat film is deposited on the loading table in the film forming device and a TiN film is immediately formed at a process temperature of about 680° C. and thereafter, when the loading table is conditioned at about 680° C. for 17 hours and then a film is formed. The drawing shows that the specific resistance of the TiN film after conditioning for 17 hours is reduced about 50 μΩ·cm compared with that before conditioning. This means that as converted to a wafer temperature, the temperature after conditioning for 17 hours is higher by about 20° C.
In view of such a matter, conventionally, during a period of idling of the film forming device as mentioned above, the temperature of the loading table is lowered to about 300 to 500° C. and further inert gas such as N2 gas is fed, thereby the degeneration of the precoat film causing instability of the wafer temperature is prevented.
As a result, the temperature changing operation and temperature stabilization operation of the loading table require a lot of time and even if it is intended to restart the film forming process, a quick process cannot be performed and a large decrease of the throughput is caused.
The present invention has been developed to solve the aforementioned problems effectively by taking notice of them. An object of the present invention is to provide a precoat film forming method, a loading structure, and a film forming device for not requiring to lower the temperature of a loading table even during a period of idling by stabilizing a precoat film, thereby improving the throughput.
Meanwhile, in making the TiN films deposit on wafers practically, it is required that the TiN films formed on the wafers processed one by one successively have a substantially constant film thickness with high accuracy in view of an improvement in the electrical characteristics of a semiconductor integrated circuit. In other words, it is necessary to maintain the uniformity (or called “reproducibility”) in film thickness among respective surfaces of the wafers highly.
Nevertheless, in the conventional processing apparatus, it has not been attempted to take a lot of time for the formation of a precoat film in order to enhance the operating rate of the apparatus. For example, by the previously-mentioned thermal CVD, a precoat film having the order of 0.2 μm in film thickness has been formed up to now.
In this case, however, if the formation process of TiN films on semiconductor wafers is started after the formation process of the precoat films has been completed and successively stabilized, then there arises a problem that the film thickness of TiN films formed on some wafers processed initially varies in instability.
The present invention has been developed to solve the aforementioned problem effectively by focusing attention on it. An object of the present invention is to provide a loading table capable of thermal stability, thereby making an excellent reproducibility in terms of film thickness, and further provide a processing apparatus and a processing method.
As a result of studying a precoat film formed on the loading table diligently, the inventors of the present invention have obtained a knowledge that, if only forming a precoat film of film thickness so as to attain a generally constant radiation heat quantity from the loading table, it is possible to improve the reproducibility of film formation since the thermal stability is maintained at the subsequent film-forming process on the semiconductor wafers, thereby accomplishing the present invention.
Another object of the present invention is to provide an idling method of a film forming device for feeding predetermined gas during a period of idling without stabilizing a precoat film, thereby not requiring decreasing of the temperature of a loading table even during a period of idling, thereby improving the throughput.
On the other hand, there is the following problem imposed also regarding the film forming method for a semiconductor wafer.
Namely, when a film is to be deposited on the surface of a semiconductor wafer, in order to keep the electric characteristics of the deposited film uniform, it is necessary to deposit a film in the same condition always or everyday and maintain the reproducibility highly. In a semiconductor wafer processing device represented by a film forming device, even if the same process conditions are set, the operation condition of the processing device itself may be varied delicately with various factors, so that periodically or non-periodically, for example, a film is deposited on a test semiconductor wafer every morning and the sheet resistance is measured, and the operation condition of the processing device at that time is checked.
Further, also to maintain the electric characteristics of the semiconductor integrated circuit itself as designed, it is desirable that a deposited film maintains the sheet resistance which is a desired value.
Meanwhile, although it is desirable that the sheet resistance of a deposited film is always constant ideally, actually, it is found that according to the process temperature at film forming time and the conditioning time from film forming to measurement of the sheet resistance, the sheet resistance itself is changed greatly and the change with time is large. The cause is seemed to be that the deposited film is oxidized by H2O or O2 in the atmosphere.
As a result, even if the sheet resistance of a deposited film of a test wafer is measured and checked every morning in order to ascertain the operation condition of the film forming device, when the time from film forming to measurement is varied with a day, for example, even when the film forming device itself is operated under the same condition, the sheet resistance is greatly shifted and as a result, a problem arises that the film forming device is adjusted unnecessarily or a reverse case occurs.
When the sheet resistance itself of a deposited film is varied with time like this as mentioned above, a problem arises that it is difficult to manufacture a semiconductor integrated circuit as designed.
This respect will be explained hereunder by referring to FIGS. 8 and 9. FIG. 8 is a graph showing the relationship between the process temperature at the time of forming a TiN film and the oxygen (O) concentration in the film after conditioning for three days in the atmosphere after film forming. FIG. 9 is a graph showing the process temperature at the time of forming a TiN film and the change rate of the sheet resistance after conditioning for three days in the atmosphere after film forming. The graph in FIG. 8 shows that when the process temperature is about 530° C., the oxygen concentration after three days is considerably high such as 4 atms %, while when the process temperature is about 700° C., the oxygen concentration after three days is considerably low such as 1.5 atms %.
FIG. 9 shows the ratio of the sheet resistance immediately after film forming to the sheet resistance three days after the film is conditioned for three days in the atmosphere, and when the process temperature is about 530° C., the sheet resistance after three days is increased to about two times (100%), and when the process temperature is about 700° C., the sheet resistance after three days is decreased to about 1.1 times (10%), and in either case, the change rate is higher than 5% which is a target, and it is desired to suppress this change rate smaller early.
The present invention has been developed to solve the aforementioned problems effectively by taking notice of them. An object of the present invention is to provide a film forming method for suppressing the change with time of the sheet resistance greatly.